49 / 2023-12-27 12:23:32

Coalbed Methane Reservoir Properties Evaluation and 3D Static Modeling for Sweet-Spot Prediction in Dahebian Block, Guizhou Province, China

Coalbed methane; reservoir properties; 3D static modeling; sweet-spot prediction.

Guizhou Province has many multi-layer, thin-thick coal seams; however, complex geology, incomplete reservoir characterization, and sweet-spot selection technology prevent large-scale coalbed methane (CBM) development. This study evaluates the CBM reservoir properties of the Dahebian block utilizing logging data from 23 wells, coal samples, and well testing data from well DH-1. Based on reservoir property assessment, a 3D static model was created to evaluate spatial distribution and propagation. Finally, a comprehensive evaluation score was obtained using a multi-level fuzzy method using nine parameters derived from the 3D model. The coal measure strata have 22 deeply buried coal seams, although seams >2 m thick have 2 or 3 thin non-coal layers intercalated. Coal seams 1^#, 7^#, and 11^# are widely distributed and have high gas saturation and gas content, which increases along the syncline axis. Moreover, the southern and central parts of coal seam 7^# and 11^# have less tectonically deformed coal (TDC), whereas cataclastic TDC dominates. The coal seam 11^# has good permeability compared to others; also, it is relatively high, where the degree of TDC development is low. The reservoir pressure gradient and coefficient indicated seams 1^# and 7^# are low-pressure, and 11^# is a normal pressure anomaly reservoir. The sweet-spot evaluation score for coal seam 1^#, 7^#, and 11^# commingled CBM development is 0.64-0.88. Comparing Zhongshan Dahebian CBM development data with evaluation scores shows areas with scores <0.78, ≥0.78-≤0.84, and >84 produced an average of <300m³, 300-500m³, and >500m³ of CBM daily, respectively. The research area has a high potential sweet spot for commingled production in the south (evaluation score >0.84), medium potential sweet spot in the center and south-eastern areas (≥0.78 to ≤0.84), and low potential in the western and northern parts (<0.78). This study validates CBM development statistics, identifies future development areas, and provides the basis for geologically complex Guizhou CBM development.